1. Field of the Invention
The present invention relates to a method of manufacturing a dielectric waveguide suitable for use as a transmission waveguide in the millimeter-wave band and microwave band, and for use in an integrated circuit, and a dielectric waveguide obtained by the manufacturing method.
2. Description of the Related Art
An example of a dielectric waveguide comprises a dielectric strip provided between two conductive planes, which are substantially parallel, so that electromagnetic waves are transmitted along the dielectric strip. One dielectric waveguide, a non radiative dielectric waveguide (referred to as xe2x80x9cNRD guidexe2x80x9d hereinafter) is developed as a transmission waveguide exhibiting less transmission loss, in which the distance between the two conductive planes is set to be a half or less of the wavelength of the transmitted wave to form a cut-off region, for preventing radiation of electromagnetic waves from the dielectric strip. The electromagnetic wave propagation modes of such NRD guides include two types including an LSM mode and an LSE mode, and the LSM mode exhibiting less loss is generally used.
FIGS. 3 and 4 are sectional views respectively showing the two typical constructions of conventional NRD guides.
FIG. 3 shows a normal type NRD guide 1 comprising a dielectric strip 4 provided between two conductive plates 2 and 3 which are arranged in parallel to each other. This normal type NRD guide 1 is disclosed in, for example, Japanese Examined Patent Publication No. 62-35281.
FIG. 4 shows a so-called winged type NRD guide 5 in which wings 8 and 9 are integrally formed on dielectric strips 6 and 7, respectively, and conductors 10 and 11 are provided on the surfaces of the dielectric strips 6 and 7, and the wings 8 and 9, respectively, which face outward, the two dielectric strips 6 and 7 being arranged opposite to each other. The conductors 10 and 11 can be formed by, for example, an evaporation method, a method of baking conductive paste containing silver or the like. Such a winged type NRD guide 5 is disclosed in Japanese Unexamined Patent Publication No. 6-260814.
In the winged type NRD guide 5, the conductors 10 and 11 can be easily aligned with the dielectric strips 6 and 7, respectively, as compared with the normal type NRD guide 1, and the winged type NRD guide 5 has the advantage of excellent reproducibility of characteristics.
Examples of materials for the dielectric strips include synthetic resins such as Teflon (registered trademark of U.S. Du Pont), and the like, and dielectric ceramic. The dielectric ceramic has a higher dielectric constant than a synthetic resin, whereby the bend loss of curved portions of the dielectric strips can be decreased, and miniaturization can be achieved. Therefore, at present, development of a dielectric strip using dielectric ceramic is proceeding.
In the winged type NRD guide 5 shown in FIG. 4, the width W of each of the dielectric strips 6 and 7, and the thickness T of each of the wings 8 and 9 are defined by the dielectric constant of the dielectric material, which constitutes these components, and the frequency of the electromagnetic wave used. Each of the width w and the thickness T generally decreases as the dielectric constant or the frequency used increases.
The dielectric strips 6 and 7 and the wings 8 and 9 of the winged type NRD guide 5 shown in FIG. 4 are produced by using dielectric ceramic and one of two methods: a first conventional method comprising cutting a plate-shaped ceramic sintered body obtained by firing, to impart the shapes of the dielectric strips 6 and 7 and the wings 8 and 9 to the ceramic sintered body, or a second conventional method comprising laminating a plurality of green sheets including green sheets each comprising an opening or notch, which is previously provided for making the wings 8 and 9 thinner than the dielectric strips 6 and 7, and then firing the resultant green sheet laminate to form the dielectric strips 6 and 7 and the wings 8 and 9, each having the desired shape, as disclosed in Japanese Unexamined Patent Publication No. 10-224120.
However, in the first conventional method, the fired ceramic sintered body is very hard, thereby causing the problem of requiring much time and labor for cutting the ceramic sintered body in the desired shape. Also, each of the wings 8 and 9 has a relatively small thickness T, thereby causing the problem of easily producing cracking or chipping during the cutting step.
On the other hand, in the second conventional method, it is very difficult to precisely cut the green sheets to the width W of the dielectric strips 6 and 7, and to precisely align the plurality of green sheets, thereby causing the problem of poor workability. Particularly, a NRD guide frequently used as a radio frequency transmission waveguide is required to have very high dimensional precision for the dielectric strips, and thus the problem of poor workability becomes serious.
The present invention provides a method of manufacturing a dielectric waveguide with reduced the manufacturing cost, with increased dimensional precision in the dielectric strips and wings, and with less cracking or chipping in the course of the processing process, and a dielectric waveguide obtained by the manufacturing method.
The present invention is aimed at a method of manufacturing a winged type NRD guide comprising a plurality of conductors having substantially parallel planes, a dielectric strip arranged between the planes of the plurality of conductors, and a wing integrally formed to extend from the dielectric strip along each of the planes of the conductors. In order to resolve the above technical problems, the method of manufacturing a dielectric waveguide of the present invention is characterized by the following construction.
In a first aspect of the present invention, the manufacturing method comprises the step of preparing a green compact containing an inorganic powder and an organic binder for forming a dielectric strip and a wing by using a part of the green compact, the step of forming a resist material on the outer surface of the green compact with an opening formed at a position of the resist material corresponding to the wing, the step of removing the portion of the green compact, which is exposed through the opening, to a desired amount by using the resist material as a mask to form an unfired structure having the shapes of the dielectric strip and the wing, the step of removing the resist material, the step of firing the structure to obtain a sintered body having the dielectric strip and the wing, the step of providing a conductor on the surfaces of the dielectric strip and the wing, which face outward, and the step of arranging two sintered bodies in a state in which the dielectric strips are opposed to each other.
The method of manufacturing a dielectric waveguide in the first aspect of the present invention further comprises, in the step of removing the portion of the green compact exposed through the opening, the step of preparing a difficult-to-remove material having a lower removal rate than that of the green compact, to provide a removal inhibiting layer comprising the difficult-to-remove material in a portion of the green compact corresponding to the thickness of the wing in preparing the green compact, so that the step of removing the portion of the green compact exposed through the opening is carried out until the removal inhibiting layer is exposed.
In the first aspect of the present invention, in preparing the green compact, a plurality of green sheets containing an inorganic powder and an organic binder are preferably prepared and laminated.
In a second aspect of the present invention, the manufacturing method comprises the step of preparing a sintered ceramic substrate for forming a portion of a dielectric strip and a wing, the step of preparing a green sheet containing an inorganic powder and an organic binder for forming the remainder of the dielectric strip, the step of fixing the green sheet on the ceramic substrate, for preparing a composite laminate, the step of forming a resist material on the outer surface of the composite laminate with an opening formed at a position of the resist material corresponding to the wing, the step of removing the portion of the green sheet, which is exposed through the opening, to a desired amount by using the resist material as a mask to form an unfired structure having the shapes of the dielectric strip and the wing, the step of removing the resist material, the step of firing the structure to obtain a sintered body having the dielectric strip and the wing, the step of providing a conductor on the surfaces of the dielectric strip and the wing, which face outward, and the step of arranging two sintered bodies in a state in which the dielectric strips are opposed to each other.
The method of manufacturing a dielectric waveguide in the second aspect of the present invention further comprises, in the step of removing the portion of the composite laminate exposed through the opening, the step of preparing a difficult-to-remove material having a lower removal rate than that of the green sheet, to provide a removal inhibiting layer comprising the difficult-to-remove material between the ceramic substrate and the green sheet in the composite laminate in preparing the composite laminate, so that the step of removing the portion of the composite laminate exposed through the opening is carried out until the removal inhibiting layer is exposed.
In the second aspect of the present invention, the ceramic substrate and the green sheet preferably contain the same ceramic material.
In the step of fixing the green sheet on the ceramic substrate, a plurality of green sheets are preferably laminated on the ceramic substrate with the removal inhibiting layer provided therebetween.
In the green compact in the first aspect of the present invention or the composite laminate in the second aspect of the present invention, the step of removing the portion exposed through the opening is preferably carried out by a sand blasting method.
In the use of the sand blasting method, the removal rate of a material to be removed by the sand blasting method generally increases as the hardness of the material increases. Therefore, the removal inhibiting layer preferably comprises a softer material than the green compact or the green sheet. Therefore, the difficult-to-remove material which constitutes the removal inhibiting layer can be easily realized by a composition containing a larger amount of organic component than the green compact or the green sheet. The difficult-to-remove material preferably contains substantially no inorganic component.
In both the first and second aspects of the present invention, the step of removing the resist material is preferably carried out at the same time as the step of firing the structure.
The present invention also provides a dielectric waveguide obtained by the above-described manufacturing method.